The present invention relates to recording apparatuses and more particularly, to the recording controls of a thermal recording apparatus which is capable of recording middle tones.
Conventionally, dither method is known as one method for displaying middle tones. In this known method, middle tones are displayed on the basis of the density of dots per unit area. For example, in the case where a unit area has 16 (=4.times.4) dots, it is possible to obtain 16 gradations. Namely, in known thermal recording apparatuses, recording is performed in which two values, i.e. "1" for performing printing and "0" for preventing printing are merely allotted to each heating element. In the known thermal recording apparatuses, in order to display middle tones (color density) by these two values, a set of a plurality of dots, (i.e. dots having a matrix of 4.times.4) are used as one picture element such that middle tones are recorded by changing, in the dots of the picture element, a ratio of the number of dots to be printed to the number of the remaining dots not to be not printed.
However, in the prior art thermal recording apparatuses referred to above, since one gradation in the picture element (4.times.4 dots) corresponds to an area of one dot, display of the number of gradations is restricted, to 16 ways by the area of the dots (4.times.4 dots). Thus, the prior art thermal recording apparatuses have such a drawback that gradations cannot be displayed sufficiently.
In order to obviate the above described drawback of the prior art thermal recording apparatuses, such a recording method is recently proposed in which a recording paper sheet is fed through an interval of a half of the area of one dot at the time of recording scanning of each line of the recording paper sheet so as to be scanned for recording at the feeding interval of a half of the area of one dot such that gradations with a higher resolution can be displayed. However, in the case where color recording is performed by this method, such a problem arises that since all hues of yellow (Y), magenta (M), cyan (C) and black (BK) are scanned at an identical recording speed, a long time period is required therefor.
It should be noted that the hues of Y, M, C and BK are not necessarily required to be printed at an identical speed (identical gradation). Printing the hue of BK at a higher speed (lower gradation) than the hues of Y, M and C offers no problem for practical recording of images.